1. Field of the Invention
The present invention relates to an electron spectrometer of the type in which a substance under investigation is bombarded with electrons and the spectra of electrons scattered from the substance are studied. Spectrometers of this type are used to investigate for example the atomic and molecular structure of materials. The substance which is bombarded with electrons is generally referred to as the target.
The basic principles of electron spectrometry are well known and a useful description of these principles is contained in U.S. Pat. No. 3,777,159. In conventional electron spectrometers, a beam of electrons provided by an electron source is initially dispersed in energy. A monochromatic beam (in which all the electrons have the same energy) is selected from the dispersed output of the electron source and the monochromatic beam is used to bombard a target. A beam of scattered electrons results the energies of which vary and this beam of scattered electrons is in turn dispersed in energy and detected by a linear array of detectors. The output of each detector is representative of the number of electrons scattered from the target having an energy corresponding to the position of that detector.
It has been proposed to provide two dimensional electron spectrometers in which the single linear array of detectors provided in one dimensional spectrometers is replaced by a two dimensional array made of a series of arrays of detectors arranged in parallel. In one known electron spectrometer the detectors are in the form of a 100.times.100 photodiode array. In all the known electron spectrometers however, the target is bombarded with a monochromatic beam of electrons so that appropriate conclusions can be drawn from the detected energy of the resultant scattered electrons. The use of a monochromatic beam does however mean that only a small proportion of the output of the electron source is in fact utilized to bombard the target.